1. Technical Field
The present invention relates to a method for foaming a high-viscosity material and an apparatus therefor. Specifically, the present invention relates to a compact and simple apparatus for foaming a high-viscosity material, which is used for forming a foamed-in-place gasket, filling of a void, etc.
2. Description of the Related Art
FIG. 5 shows a fluid circuit of a gas mixing/supplying device of a conventional foaming apparatus. In this gas mixing/supplying device, a gas is introduced into a high-viscosity material by means of a piston pump. FIG. 6 is a front cross-sectional view indicating a structure of a piston pump used in conventional techniques. FIG. 7 is a timing chart for explaining an operation of the piston pump.
In FIG. 5, a gas introducing device 212 comprises two piston pumps 245A and 245B which operate in an alternate manner. In each of the piston pumps 245A and 245B, a piston is operated by means of a motor M2A or M2B so as to effect a reciprocal linear movement of the piston. Thus, the piston is reciprocally moved in the cylinder, to thereby effect a suction stroke and a discharge stroke. The piston pumps 245A and 245B are interposed between conduits 239A and 244A. A high-viscosity material MV supplied from a high-viscosity material supply device 211 and a gas supplied from a gas supply device 210 are individually introduced to the piston pumps at a predetermined ratio in a batchwise manner. As shown in FIG. 6, a piston pump 245 comprises a cylinder 451, a piston 452 which fittingly slides in the cylinder 451, and 3 needle valves NV1, NV3 and NV5 provided in the cylinder 451.
As shown in FIG. 7, in either the piston pump 245A or the piston pump 245B, the piston moves from a discharge end to a suction end, thus effecting a suction stroke. During this time, after lapse of time T1′ from the start of movement of the piston, the needle valve NV1 is opened, and a gas is supplied to the piston pump. Time T1′ is about 1 to 2 seconds. During time T1′, an inside of the cylinder is subject to negative pressure.
Soon after the piston reaches the suction end, the needle valve NV1 is closed. Thus, after completion of the suction stroke, the inside of the cylinder 451 is filled with a gas having controlled pressure. After lapse of time T3′ after the needle valve NV1 is closed, the needle valve NV3 is opened. Time T3′ is about 0.1 to 0.5 second. With this arrangement, the needle valve NV1 and the needle valve NV3 are prevented from being open simultaneously. During time T4′ during which the needle valve NV3 is open, by means of a screw pump rotatingly driven by the motor M1A, a high-viscosity material MV from the high-viscosity material supply device 11 is supplied into the cylinder 451. Due to a high pressure of the high-viscosity material, a gas having a predetermined pressure, which has been preliminarily supplied into the cylinder 451, is compressed in a ratio equal to a pressure ratio between the high-viscosity material and the gas. Consequently, a volume of the gas becomes substantially negligible.
After lapse of time T5′ after the needle valve NV3 is closed, the needle valve NV5 is opened. The piston 452 moves from the suction end to the discharge end, thus effecting a discharge stroke. Time T5′ is about 0.1 to 0.5 second. During the discharge stroke, the needle valves NV1 and NV3 are closed, with forward end portions of the needle valves being flush with an inner circumferential surface of the cylinder 451. Therefore, no dead space is formed, and the gas and the high-viscosity material filled in the cylinder 451 are completely discharged from an opening 454 of the needle valve NV5. After lapse of time T6′ after completion of the discharge stroke, a subsequent suction stroke is started. Time T6′ is about 0.1 to 0.5 second.    Patent Document 1: Japanese Patent Public Disclosure No. 09-206638    Patent Document 2: Japanese Patent Public Disclosure No. 10-272344    Patent Document 3: Japanese Patent Public Disclosure No. 10-278118